The electric shower is hugely popular because it is easy to install due to its multiple cable and water entry points which make it ideal for replacing an existing shower as there is little need to make new holes in the wall for installation. They only require a mains cold water supply as the water is then heated quickly by passing over an element inside the unit, so therefore doesnt use any stored water. Electric showers also dont require a pump as the water pressure depends on the pressure of your mains. There are a range of wattage options and the general rule is the higher the wattage, the more powerful the waterflow. It is strongly recommended that a qualified person install these as electrical work will be involved.